The present invention relates, in general, to integrated circuits and, more particularly, to integrated mixer circuits for providing frequency translation in a heterodyne receiver.
In electronic systems such as cellular or wireless telephones, a signal generated by a Local Oscillator (LO) is selected to operate at a frequency that allows tuning of an incoming signal. The incoming signal can be a modulated signal containing information that is recovered in a receiver of the electronic system. The modulated signal and the signal generated by the LO are mixed to translate the carrier frequency of the modulated signal from the Radio Frequency (RF) range to a signal having frequencies in an Intermediate Frequency (IF) range.
Generally, the signal generated by the LO has a large amplitude compared to the amplitude of the received modulated signal. The amplitude of the signals received by the receiver are adjusted by amplifiers. In addition, some receivers such as a heterodyne receiver, include passive filters that reject unwanted images. Any inaccuracies in amplitude and phase shifting generate an undesired component during translation of the modulated signal. Thus, accurate amplitude and phase shifting are necessary for preventing an undesired image signal and allowing the information in the modulated signal to be recovered and the image signals to be canceled.
However, it is difficult to maintain equivalent signal attenuation through the mixers as well as linearity in the phase shifters capable of generating a phase relationship of one hundred and eighty degrees. Voltage and temperature changes in a heterodyne receiver cause signal distortions in phase shifters operating over a wide frequency range.
Accordingly, it would be advantageous to have a method and a receiver circuit for translating the frequency of an incoming modulated signal. It would be of further advantage to have the receiver circuit operate with an LO signal that is converted to differential signals having an accurate phase relationship over a wide range of operation.